In a watch with a quartz movement, when the rotor of the stepping motor makes one step, a display member, generally a hand, makes a pivoting movement through a given angular step of a few degrees. At the end of this pivoting movement, the hand stops, and the stopping is generally accompanied by an oscillation, which may be visually unpleasant for the user, particularly when the pivoting movement of the hand is slow, such as during display of a particular function, for example a compass function, with a single phase motor. It is known to reduce or remove this oscillation by inserting an elastic friction washer in the gear train, to create continuous friction which completely damps the oscillation, but at the cost of a subsequent excessive use of energy, and thus a loss in efficiency.
Another method of removing the oscillation defect is for the hand to perform a rapid movement, so that it then no longer has time to oscillate at the end of each step. However, this rapid movement cannot be achieved with a single phase motor, of the type conventionally used to drive the display member when implementing a particular function, other than the time display.
The general problem which arises is improving the coupling between a plurality of display members, particular two display members, with the lowest possible loss of energy, both during the coupling and the separation of the display members.
It is known to form a mechanical coupling between display members, particularly by friction, and more particularly using one or several springs. FR Patent No. 2 256 459 in the name of TIMEX CO. thus discloses a time zone mechanism with a coupling and a spring stop. GB Patent No. 731 689 in the name of HAMM discloses the synchronous driving of a second set of hands for setting an alarm, via the main set of hands, after the change from the alarm time, using springs.
EP Patent No. 1 916 574 in the name of VAUCHER S A discloses an indicator hand for displaying several pieces of information, comprising a first index portion corresponding, for example, to a conventional time display, hinged to a second index portion, which is provided with a radial or conical toothing and intended to be driven by the pivoting movement about a second axis of rotation perpendicular to the first axis of rotation about which the first index portion pivots.
Various types of magnetic coupling have been displayed for particular applications, and always between a motor means and a single display member. CH Patent No. 528 765 dated 1972 in the name of OMEGA S A discloses a mechanism for changing the indication of the hour hand by the stem, without any additional push-buttons. This mechanism includes a bottom motion-work hand controlling the hour hand via a motion-work pinion. The arbour of this pinion carries a loosely mounted top wheel, which is coaxial to and magnetically positioned relative to a bottom wheel and is actuated by the movement. The bottom wheel is controlled by the stem to rotate the hour hand without affecting the indication of the other hands. A flat spring including a ramp tends to push the top wheel towards the bottom wheel, via a bearing plate which rests on the top wheel via a metal foil with star-shaped resilient arms. The position of the stem controls the pivoting of a lever, one arm of which cooperates with the ramp of the flat spring, to allow, according to the position of the stem, the top and bottom wheels to move further apart or closer together. The friction applied by the metal foil is greater than the magnetic coupling force between the top and bottom wheels. The bearing plate includes posts which pass through and trap the top wheel and can cooperate with passages comprised in the bottom wheel to drive said wheel by mechanical coupling in the set-hands position. The springs introduce resistant stresses into the mechanism which adversely affect its efficiency.
JP Patent Application No. 58 097 682 in the name of SEIKOSHA discloses the driving of hands by magnetic coupling with the wheels, in a configuration which means that the movement is very thick.
DE Patent No. 254 7657 in the name of JUNG discloses a conventional timepiece mechanism driving hands hidden behind a plate, the end of each hand is magnetised and attracts a ball through the plate. Only the ball can be seen by the user. U.S. Pat. No. 3,701,252 in the name of TAKESHI OKAMOTO discloses a similar system.
EP Patent Application No. 0 308 243 in the name of SEIKO discloses a magnetic coupling on a display element which causes indices to appear in the form of balls enclosed in a chamber pressed against an aperture, or which starts the movement of a decoration mounted on a spring upon the passage of the poles of a magnetic element, rotor or hand.
However, although solutions are found for driving or displaying a display member, the prior art does not propose any indexing between two display members of different sizes.